Alienware showed off their Steam PC running Steam OS at CES 2014, but didn't explain many details. The specifications for the device aren't yet announced, but it is announced that it will have an Intel CPU and NVIDIA GPU. Pricing is said to be around $450 to $600, possibly more with larger configurations. This is all speculation of course, but you can explore more from the FAQ page over at Alienware's website.
Alienware Steam Machine Landing Site: http://www.alienware.com/Landings/steammachine/
More updates to come on this machine and more as the specs and information develops.